Stressing Out the Poor

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16 Pathways Winter 2011

Stressing Outthe Poor

Chronic Physiological Stress andthe Income-Achievement Gap

By Gary W. Evans, JEannE Brooks-Gunn,

and PamEla kato klEBanov


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Pathways Winter 2011

It is well known that economic depriva-

tion early in lie sets children on a tra-

jectory toward diminished educational

and occupational attainment. But why is

early-childhood poverty so harmul? I we

cant answer that question well, our reorm

eorts are reduced to shots in the dark.

In this article, we oer a new perspective on this

question. We suggest that childhood poverty is

harmul, in part, because it exposes children to

stressul environments. Low-income children

ace a bewildering array o psychosocial and

physical demands that place much pressure on

their adaptive capacities and appear to be toxic

to the developing brain. Although poor childrenare disadvantaged in other ways, we ocus our

analysis here on the new, underappreciated path-

way depicted in Figure 1. As shown in this g-

ure, children growing up in poverty demonstrate

lower academic achievement because o their

exposure to a wide variety o risks. These risks,

in turn, build upon one another to elevate levels

o chronic (and toxic) stress within the body. And

this toxic stress directly hinders poor childrens

academic perormance by compromising theirability to develop the kinds o skills necessary to

perorm well in school.


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accumulation occurs in various ways; or example, children who

score poorly at age six may be tracked into low-achievement

school groups, which in turn exposes them to lower expecta-

tions, to less rigorous curricula, and to less capable peers, all o

which urther disadvantage them and generate ever more sub-

stantial between-group gaps. The RiskStress Model, to whichwe turn later, suggests that such splaying may also be attributed

to the cognitive decits and poorer health that chronic stress

generates. Both cognitive decits and ill health then repeatedly

disadvantage poverty-stricken children in one educational set-

ting ater another.

Pathway #1: Parenting PracticesWhat types o orces have social scientists conventionally under-

stood as explaining the achievement gaps illustrated in Figure

2? One reason poor children lag behind their more afuent

peers is that their parents interact with them in ways that arent

conducive to achievement. For example, psychologist Kathryn

Grant and her colleagues have documented a strong and con-

sistent relation between socioeconomic disadvantage and harsh,

unresponsive parenting. In one national dataset, 85 percent

o American parents above the poverty line were shown to be

responsive, supportive, and encouraging to their children dur-

ing inancy and toddlerhood, whereas only 75 percent o low-

income parents had the same achievement-inducing parenting

style. While most low-income parents (i.e., 75 percent) do pro-

vide adequate levels o support and encouragement, these data

reveal, then, a nontrivial dierence across income levels in the

chances that children will experience a problematic parenting

style. There is considerable evidence that at least a portion o the

cognitive developmental consequences o early childhood pov-erty is due to this dierence.

Pathway #2: Cognitive StimulationIts also well known that children rom low-income households

tend to receive less cognitive stimulation and enrichment. For

example, a child rom a low-income amily who enters rst

grade has been exposed on average to just 25 hours o one-on-

one picture book reading, whereas an entering middle-income

child has been exposed on average to more than 1,000 hours

o such reading. Likewise, during the rst three years o lie, a

child with proessional parents will be exposed to three times as

many words as a child with parents on welare.

And its not just simple parental eects that account or theachievement decit. I a child is born into a high-income amily,

he or she may also benet rom high-quality stimulation and

enrichment rom extended amily, rom siblings and riends,

and rom more ormal care providers. All o this redounds to the

benet o higher-income children while urther handicapping

low-income children.

So much or the well-known pathways by which disadvan-

tage is transmitted. We turn now to another and less-appreciated

aspect o low-income environments that may also harm cogni-

We will unpack this new RiskStress Model in the balance

o our article. However, beore doing so, its useul to rst go

over the evidence regarding the relation between poverty and

achievement and then to present some o the well-known path-

ways through which this relationship is generated. With that

background in place, we can then describe the RiskStress

Model, as represented in Figure 1.

Poverty and AchievementIt is well known that children born into low-income amilies

lag behind their middle- and upper-income counterparts on

virtually all indices o achievement. To provide one example, a

national study o elementary school children shows that childrenin the poorest quarter o American households begin kindergar-

ten nearly 10 percent behind their middle-income and afuent

classmates in math (Figure 2). Six years later, as they are about

to enter middle school, the poorest quarter o American children

have allen even urther behind, with the gap between them-

selves and their most afuent schoolmates nearly doubling.

The splaying pattern revealed here, a general one that holds

across various outcomes, may be attributed to the tendency

or advantage and disadvantage to accumulate over time. This

figure 2 Average percentile rank on Peabody Individual AchievementMath.

35

6 8 10 12

40

Highest income quartile

Third income quartile

Second income quartile

Lowest income quartile

Age of child

Scorepercentile

45

50

55

60

65

figure 1 A new pathway to account for the income-achievement gap.

Low Achievement

Source: James J. Heckman (2006). Skill Formation and the Economics o Investing in Disadvantaged

Children. Science, 312(5782): 1900-1902.

chronic StreSSPoverty cumuLAtive riSk exPoSure


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tive development. The key concern here: Children rom impover-

ished households ace a wide array o physical and psychosocial

stressors. Their homes, schools, and neighborhoods are much

more chaotic than the settings in which middle- and upper-

income children grow up. Such conditions can, in turn, produce

toxic stress capable o damaging areas o the brain known tounderlie cognitive processessuch as attention, memory, and

languagethat all combine to undergird academic success. In

the pages that remain, we document each o the steps in the

RiskStress Model.

Poverty and Cumulative Risk ExposureThe stressors that poor children ace take both a physical and

psychosocial orm. The physical orm is well documented; poor

children are exposed to substandard environmental conditions

including toxins, hazardous waste, ambient air and water pollu-

tion, noise, crowding, poor housing, poorly maintained school

buildings, residential turnover, trac congestion, poor neigh-

borhood sanitation and maintenance, and crime. The psycho-

social orm is also well documented; poor children experience

signicantly higher levels o amily turmoil, amily separation,

violence, and signicantly lower levels o structure and routine

in their daily lives.

An important aspect o early, disadvantaged settings may be

exposure to more than one risk actor at a time. A powerul way

to capture exposure to such multiple sources o stress and strain

is the construct o cumulative risk. Although there are various

ways to quantiy cumulative risk, one common approach is to

simply count the number o physical or psychosocial risks to

which a child has been exposed. In one UK study, the authors

counted how oten children were exposed to such stresses as(a) living with a single parent, (b) experiencing amily discord,

(c) experiencing oster or some other orm o institutional care,

(d) living in a crowded home, and (e) attending a school with

high turnover o both classmates and teachers. It was ound in

this study that inner-city children experienced ar more o these

stresses than did the better-o working-class children. The same

result holds in the United States (see Figure 3). In rural New

England, only 12 percent o middle-income nine-year-olds expe-

rienced three or more physical and psychosocial risk actors,

whereas nearly 50 percent o low-income children crossed this

same threshold (o three risk actors).

In a national U.S. sample o premature and low birth weight

inants, Brooks-Gunn and colleagues similarly ound thatinants born into low-income amilies experienced nearly three

times more risk actors than their middle-income counterparts

by the time they were toddlers. These same low-income toddlers

were seven times more likely than their afuent counterparts

to experience a very high number o risk actors (> 6). The pat-

tern is overwhelmingly clear: Being born into early poverty oten

means exposure to many more physical and psychosocial risk

actors.

figure 4 Resting blood pressure in nine-year-old, White rural children.

figure 5 Overnight stress hormones in nine-year-old, White rural childr

figure 3 Cumulative risk exposure among low- and middle-incomerural nine-year-olds.

0

0 1 2 5 63 4

10

number of cumulAtive riSkS

percentAgeofSchoolchildren

expoSed

20

30

40

50

60

Poverty

Middle-Income

Note: Cumulative risks include amily turmoil, violence, child separation rom amily, noise, crowding

and housing quality.

Source: Gary W. Evans and Kimberly English. 2002. The Environment o Poverty: Multiple Stressor

Exposure, Psychophysiological Stress, and Socioemotional Adjustment. Child Development, 73(4):1

Source: Gary W. Evans and Kimberly English. 2002. The Environment o Poverty: Multiple Stressor E

sure, Psychophysiological Stress, and Socioemotional Adjustment. Child Development, 73(4):1238-

Source: Gary W. Evans and Kimberly English. 2002. The Environment o Poverty: Multiple Stressor E

sure, Psychophysiological Stress, and Socioemotional Adjustment. Child Development, 73(4):1238-

10099.5

99

100.5

101

102.5

102

101.5

poverty middle income

58

57

59

57.5

58.5

59.5

61

60.5

60

poverty middle income

diastolic

cortisol epinephrine norepinephrine

systolic

mm/hg

ug/mgc

reAtine

ng/mgc

reAtine

ng/mgc

reAtine

.01

0

.02

.005

.015

.025

.035

.03

poverty middle

income

6

5

4

3

2

1

0

poverty middle

income

33

32

31

30

29

poverty middle

income


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Cumulative Risk Exposure and Chronic StressBut does such dierential exposure indeed result in higher

stress levels among poor children? The simple answer is that it

does. In cross-sectional analyses o 9- and 13-year-old children,

Evans and colleagues ound that the risk exposure described

in Figure 3 elevated baseline, resting blood pressure as well as

overnight indices o such stress hormones as cortisol. At age 13,

when challenged by mental arithmetic problems, children with

higher levels o cumulative risk exposure did not show a typi-

cal healthy response, instead exhibiting a muted rise in blood

pressure. These same children also didnt recover as successully

rom the mental challenge posed by these arithmetic problems(as indexed by the longer time it took their blood pressure to

return to pre-stressor baseline levels). The evidence thus sug-

gests that children exposed to high levels o cumulative risk are

less ecient both in mobilizing and then shutting o physi-

ological activity.

The RiskStress Model, as represented in Figure 1, implies

that the eect o amily poverty on stress is mediated by risk

exposure. Although one would ideally like to test that mediation,

its also important to simply document the association between

poverty and stress (thereby ignoring the mediating actor). Many

investigators have indeed documented that disadvantaged chil-

dren have higher chronic physiological stress levels, as indicated

by elevated resting blood pressure. A smaller number o studies

have also uncovered higher levels o chronic stress hormones,

such as cortisol, among disadvantaged children. To provide just

a ew examples, Figures 4 and 5 show elevated resting blood

pressure as well as higher overnight urinary stress hormones in

a sample o nine-year-old rural children.

The oregoing data, which pertain to nine-year-olds, dont

tell us when such stress symptoms emerge. Do poverty-stricken

children show evidence o elevated stress early on in their lives?

Or do such symptoms only emerge later? With support rom

the Stanord Center or the Study o Poverty and Inequality, we

sought to answer this question by reanalyzing a national data set

o very young at-risk children. The Inant Health and Develop-

ment Program (IHDP) is a representative sample o low birth

weight (< 2500 grams) and premature (< 37 weeks gestational

age) babies born in 1985 at eight medical centers throughout

the country. This sample o nearly 1,000 babies is racially and

economically diverse (52 percent Black, 37 percent White, 11 per-

cent Hispanic).

We assessed resting blood pressure and childs height and

weight at 24, 30, 36, 48, 60, and 78 months o age. The collec-tion o physical health data at such young ages and over time

provided us with an unprecedented opportunity to examine the

early trajectories o chronic stress among a high-risk sample

o babies. Both baseline blood pressure levels and Body Mass

Index (BMI) refect wear and tear on the body and are precur-

sors o lielong health problems. The ormer is indicative o car-

diovascular health and the latter o metabolic equilibrium. BMI,

which refects at deposition, is measured as height divided by

weight (kg/m2).

We sought to assess whether these two measures o stress

are elevated in poverty-stricken neighborhoods. Low-income

neighborhoods, as dened in our study, have median household

incomes below $30,000 (in 1980 dollars), while middle income

neighborhoods have median income levels exceeding $30,000

per household. As is evident in Figures 6 and 7, babies grow-

ing up in low-income neighborhoods have health trajectories

indicative o elevated chronic stress. Additional statistical con-

trols or inant birth weight, health, and demographic character-

istics did not alter these trajectories. These gures also reveal,

even more importantly, that elevated stress emerges very early

or children growing up in low-income neighborhoods. BMI,

figures 67 Developmental trajectories in chronic stress in relation to neighborhood poverty.

15

24 36 48 60 72

16

17

Afuent Neighbors Near Poor & Poor Neighbors

Age in monthS

bmi

50

55

24 36 48 60 72

60

65

70

dbp

Age in monthS

Afuent Neighbors Near Poor & Poor Neighbors

BMI rom 24 to 78 Months by Neighborhood Poverty Diastolic Blood Pressure rom 24 to 78 Months by Neighborhood Poverty(with controls or blood pressure method & childs state)


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ConclusionChildhood socioeconomic disadvantage leads to decits in aca-

demic achievement and occupational attainment. Its long been

argued that such decits arise because poor children are exposed

to inadequate cognitive stimulation and to parenting styles that

dont encourage achievement. We dont dispute the important

role o these two variables. But we have outlined here evidence

or a new, complementary pathway that links early childhood

poverty to high levels o exposure to multiple risks, which in

turn elevates chronic toxic stress. This cascade can begin very

early in lie. Even young babies growing up in low-income

neighborhoods already evidence elevated chronic stress. Thisstress then accounts or a signicant portion o the association

between poverty and working memory, a critical cognitive skill

involved in language and reading acquisition.

The RiskStress Model suggests that the povertyachievement

link can be broken by addressing (a) the tendency o poverty to be

associated with physical or psychosocial risks (e.g., environmen-

tal toxins, amily turmoil), (b) the eects o such risks on stress,

and (c) the eects o stress on achievement. I this model bears

up under urther testing, it would be useul to explore which o

these pathways is most amenable to intervention.

Gary W. Evans is the Elizabeth Lee Vincent Professor of Human

Ecology at Cornell University. Jeanne Brooks-Gunn is the Virginia

& Leonard Marx Professor of Child Development & Education and

Co-Director of the National Center for Children and Families at

Teachers College, Columbia University. Pamela Kato Klebanov is

a Senior Research Scientist at the National Center for Children and

Families at Teachers College, Columbia University and a Visiting

Research Collaborator at the Center for Research on Child Well-

being at Princeton University.

or example, proves to be unusually low among poor children

under ve years old, but it then takes o as these children grow

older. The blood pressure measure, by contrast, registers high

among low-income children rom almost the very beginning o

our measurements (i.e., 24 months). This research conrms,

then, that low-income children are more likely than others to

develop dangerous stress trajectories very early on in their child-hood. As we discuss below, this has proound consequences or

their likelihood o success in school and beyond.

Chronic Stress and the Achievement GapThe next and nal step in our chain model pertains to the eects

o chronic stress on achievement. Here we turn to an important

longitudinal program on poverty and the brain at the University

o Pennsylvania conducted by Martha Farah and her colleagues.

In a series o studies with multiple samples drawn rom lower-

and middle-class Black amilies in Philadelphia, Farah and col-

leagues show that several areas o the brain appear vulnerable

to early childhood deprivation. Using batteries o neurocogni-

tive tests o brain unction and brain imaging studies, Farah andother neuroscientists can map the areas o the brain that are

recruited by neurocognitive tasks. As shown in Figure 8, among

the areas o the brain most sensitive to childhood SES are lan-

guage, long-term memory (LTM), working memory (WM), and

executive control. What the graph depicts is the separation,

in standard deviation units, between a low- and middle-SES

sample o 11-year-old Black children rom Philadelphia. For this

sample, one standard deviation represents about one-th o the

total distribution o scores. Samples diering by 3.5 or more

standard deviations are virtually non-overlapping. Given that the

samples dier by about 3.5 standard deviations or all our areas

o brain unctioning, this means that there is virtually no overlap

between poor and middle-class Black children when it comesto language, long-term memory, working memory, or executive

control. Eleven-year-old Black children rom lower SES amilies

reveal dramatic decits in multiple, basic cognitive unctions

critical to learning and eventual success in society. These results

reveal the starkly cognitive oundation to the poor perormance

o low-income children.

But is this achievement gap attributable to cumulative risk and

chronic stress? With a recent ollow-up o the sample depicted

in Figures 4 and 5, Evans and colleagues have now provided the

rst test o the nal link in the RiskStress Model. The base-

line nding rom their research is that working memory in early

adulthood (i.e., age 17) deteriorated in direct relation to the num-

ber o years the children lived in poverty (rom birth through age

13). I, in other words, a child lived in poverty continuously, his

or her working memory was greatly compromised. The main

result o interest, however, was that such deterioration occurred

only among poverty-stricken children with chronically elevated

physiological stress (as measured between ages 9 and 13). That

is, chronic early childhood poverty did not lead to working mem-

ory decits among children who somehow avoided experiencing

the stress that usually accompanies poverty.

0

1

.5

1.5

2.5

2

3

3.5

4

lAnguAge ltm Wm executive

control

SdSepArAtor

figure 8 Effect sizes measured in standard deviationsof separation between low- and middle-SES

10- to 12-year-old, African American children.

Source: Martha J. Farah, David M. Shera, Jessica H. Savage, Laura Betancourt, Joan M.

Giannetta, Nancy L. Brodsky, Elsa K. Malmud, and Hallam Hurt. 2006. Childhood Poverty:

Specifc Associations with Neurocognitive Development. Brain Research,1110(1): 166-74.

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Stressing Out the Poor